An Active Turbulence Grid for Turbomachinery Flow Experiments

Quantifying and predicting the effects of freestream turbulence on the aerodynamic performance of turbomachinery flows continues to be of primary interest to advance the physical understanding and modeling of loss mechanisms. This work is motivated by the need to expose turbine flows to a wide class of inlet turbulence fields, characterized by the peculiarity of setting the turbulence intensity levels and yet tuning the turbulence scales independently. This article describes the development and experimental characterization of an active turbulence generator concept that provides the authority to enable future experimental measurements in turbine cascade rigs. The study has been conducted in an auxiliary low-speed test bench with a small cross-sectional area, testing at low Mach numbers (⁠$∼$0.05) and ambient conditions. Pressure, hot-wire anemometry, and particle image velocimetry (PIV) measurements are presented. The results indicate that the active turbulence generator is capable of generating a wide range of homogeneous and isotropic freestream turbulence. Turbulence levels in the range of 1.5–13$%$ with minimum pressure losses and a low degree of nonuniformity (<5$%$⁠) have been obtained with the ability to independently control the integral length scale within the range of 6–25 mm.